Method and apparatus for registration of web material in forming filling and sealing industrial bags

ABSTRACT

Side gusseted industrial bags are continuously (or intermittently) formed from continuous web materials, and simultaneously filled and sealed in one fast operation by the method and apparatus of this invention. The various features of the invention include a tube former which wraps the web about a shaped filling mandrel most preferably with the assistance of an air bearing, registration and tension controls to accurately maintain the register of the web in relationship to printed blocks or indicia; evacuation steps to neatly gusset the bag with or without mechanical assistance, to tighten the bag firmly about the product, and to continuously wash the inside welding surfaces thereof with a cleansing high velocity air stream to thereby retain such surfaces in a more virgin or noncontaminated welding condition; filling steps that are practiced to provide a free margin of material at the top of the bag to complement the welding and gusseting steps; and hot gas welding and chilling techniques that can provide tough welds or seals with high repeatability, and which are able to withstand the shock or weight of the product load with sufficient immediacy to enable fast production cycles.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of application Ser. No. 460,864,filed Apr. 15, 1974, now U.S. Pat. No. 3,925,963, and which divisionalapplication is a continuation-in-part of application Ser. No. 347,923,filed Apr. 4, 1973 and now abandoned.

BACKGROUND OF THE INVENTION

Any bag that is 25 or more pounds (11.35 kgs) in weight is normallyclassed as a heavy duty or industrial size bag. This class bag enjoystremendous packaging and shipping usage throughout the world. Nearly allor all of the industrial bags produced commercially prior to thisinvention have been based on a preformed or pre-made bag construction.

It would amount to very meaningful cost savings, however, if heavy dutybags could be produced on a fast in-line operation, based on a form,fill and seal concept. The prior art, however, has not provided thetechnical progress that is needed in order to make a sure andwide-spread transition from the preformed, to a in-line formed, filled,and sealed industrial bag.

Perhaps the most crucial problem, if viable technical progress is to bemade, is the need for improved methods and apparatus for forming the bagseals or welds. Achieving good sealing results has been a past problemeven as regards preformed plastic bags which require only a minimum ofsealing after filling, the majority of the seals having been pre-made bythe bag manufacturer under controllable, essentially stress free, idealconditions. For example, in the March 1968 issue of Food Engineering, itis reported at page 116 that:

"Bag damage with the all-plastic bag was considerable due to failure ofthe heat-sealed closure. The closure would open in transit, and thatwould be that. This isn't a product that can be recoopered."

The welding of heavy duty form, fill, and seal industrial bags isunderstandably even more touchy, since the process does not have thebenefit of ideal bag manufacturing conditions. There is not the luxuryof being able to form and cure the seals or welds in a stress freeenvironment. Moreover, the fresh welds must accept the stress anddistortions of the product load almost immediately, and must be formedwith extremely high repeatability and good results for commercialacceptance. Still further, the welding technique must be able tosecurely weld through heavy gusseted areas if it is to achieve truesuccess. A gusseted bag is relatively square and provides a stablepallet load, and it is essential that an industrial bag have thisquality if it is to be an optimum bag. For illustrative example, a bagof 10 mil wall thickness would be 40 mils thick in the gusseted areas,30 mils thick along the overlap or longitudinal seal, and 20 mils thickin other areas. The welding techniques must accommodate such widevariances in thickness along a single weld line. Particularly, it mustform a tough weld even at the points of abrupt thickness change, andwithout causing delineated lines of pronounced weakness or thinning.

The method and apparatus for properly side gusseting the formed, filledand sealed industrial bags is another problem area. For example, in aform, fill and seal process, the side gussets must be formed after thebag has been influenced by the distortion and weight of the productload, whereas, in a preformed bag, the side gussets can be neatly tuckedin and secured under far more compatible conditions. Particularly if aform, fill, and seal industrial bag is to be optimally suited forcommercial use, i.e., palletizing, there must be provisions forincluding functionally adequate side gussets in the ultimate bagstructure.

Still further, the desired method and apparatus for producing anacceptable form, fill and seal industrial bag, should advantageouslyprovide for flexibility in the materials from which the bag can beformed. The ultimate performance of an industrial bag, of course,depends on the materials from which it is manufactured. It is extremelydesirable, for example, that in some uses, the industrial bag beprovided with multiple plies of material to better absorb the expectedhandling abuses. Most desirably, therefore, the operation should besufficiently flexible to permit the usage of webs of multiple plies ofmaterial, together with tough scrim layers such as of fabric, nylon,rayon, and the like, that give the bag improved integrity. A multi-layerbag is generally felt to be tougher than a single ply bag of equivalentthickness, and the scrim layers can add considerable abuse resistance tothe bag.

As yet another factor to be dealt with, a prospective form, fill, andseal method and apparatus for industrial bags should, for optimumversatility, expediently prepare the bag for a post-shrinkage step. Thisflexibility will permit the bag to be tightly shrunk about the productso that it retains a firm, tight character through a normal or evenextended use period.

Accordingly, it is the primary objective of this invention to provide anapparatus and method suitable for in-line forming, filling, and sealingof industrial size bags.

It is particularly among the objectives of this invention to accomplishthe primary objective with a maximum of finesse and flexibility, wherebythe method and apparatus are advantageously designed to:

i. form exceedingly tough welds with a very high degree ofrepeatability, that can withstand the abuses of commercial handling withan acceptably low frequency of failure, and, that can withstand theweight of the product load with sufficient immediacy to enable fastproduction rates;

ii. permit manufacture of side gusseted bags with optimum palletizingand handling characteristics, and wherein the welding procedure is ableto weld through and secure the gussets strongly in the bag structure;

iii. handle excessively dusty products of the type that normally giveproblems through contamination of welding surfaces;

iv. optimize the palletizing and handling characteristics of the bag andminimize material usage, by forming a tight, firm bag about the product;

v. automatically precondition the bag for a post-shrinkage step;

vi. achieve finesse in holding and maintaining proper registration sothat the bags can be produced with accurate registration of printedblocks and indicia thereon; and

vii. fill the bags in a manner that complements the welding andgusseting of the bag with repeatedly good results, and that facilitatesthe performance of these objectives at commercially acceptablemanufacturing speeds.

Other objectives, aspects, and advantages of the invention will in partbe pointed out in, and in part apparent from, the following descriptionconsidered together with the accompanying drawings, in which:

FIG. 1 is a side elevational view illustrating apparatus for forming,filling, and sealing industrial class bags in accordance with thegeneral teachings and principles hereof, certain parts of the apparatusbeing shown in this view in generally abbreviated or schematic detail;

FIGS. 2 through 4 are views like FIG. 1, which are used to illustratethe process of the apparatus thereof, particularly in the sense ofshowing progressive stages in the filling cycle of such apparatus;

FIGS. 5 through 7 are cross-sectional views through FIGS. 2 through 4,respectively, taken along reference lines 5--5, 6--6, and 7--7,respectively;

FIG. 8 is a plan view which illustrates in somewhat more thoroughdetail, the preferred embodiment of the unwind assembly from which acontinuous web is fed to form the bags, and also partially shows thedrag inducing or applying unit associated therewith for automaticallyvarying and controlling the tension on the web;

FIG. 9 is essentially an elevational view that illustrates the dragapplying unit as viewed along reference line 9--9 of FIG. 8;

FIG. 10 is a side elevational view which illustrates in somewhat morethorough detail, the preferred embodiments of the filling mandrel, tubeformer, and vertical seam welder of the apparatus of FIG. 1;

FIG. 11 is a front elevational view of the apparatus as shown in FIG.10, except with the vertical seam welder having been broken away and notillustrated in this view;

FIG. 12 is a cross-sectional view taken along reference line 12--12 ofFIG. 10, and essentially comprises a plan view of the apparatus as shownin FIG. 10;

FIG. 13 is a plan view of the vertical seam welder of FIG. 10;

FIG. 14 is a cross-sectional view of the vertical seam welder of FIG.13, taken along reference line 14--14 thereof;

FIG. 15 is an enlarged, partial view showing the air bearing andadjusting clamp of the tube former;

FIG. 16 illustrates the vertical weld formed in the bag in a conditionimmediately after it passes the vertical seam welder and associatedchilling head; and FIG. 17 shows the same weld after having beensubjected to the shock of product load, whereby essentially all wrinklesare removed from the weld and an invisible or near invisible weld lineis achieved;

FIG. 18 is a plan view which illustrates the apparatus of FIG. 1 in morethorough detail, this view looking down into the bag sizing cage of theapparatus;

FIG. 19 is a cross-sectional view taken along reference line 19--19 ofFIG. 18, and illustrates particularly the floating pressure plateemployed to control the clamping pressure in the bag sizing cage;

FIGS. 20, 21, and 22 are front elevational, plan, and end views,respectively, which illustrate in more thorough detail, the preferredembodiment of one of the co-acting sealing heads of the apparatus ofFIG. 1, a portion of FIG. 21 being broken away to reveal the moveablecutter head carried by this sealing head;

FIG. 23 is a cross-sectional view through FIG. 21, taken along referenceline 23--23, thereof;

FIGS. 24 and 25 are front elevational and plan views, respectively,which illustrate in more thorough detail, the preferred embodiment ofthe opposite co-acting sealing head of the apparatus of FIG. 1, aportion of FIG. 24 being broken away particularly to illustrate thedetail of the hot and cold gas valves included in the design of thissealing head;

FIG. 26 is a cross-sectional view through FIG. 24, taken along referenceline 26--26, thereof;

FIG. 27 is a partial side elevational view particularly illustrating theco-acting sealing heads at a moment just prior to their engagement toform the end welds of the bag in accordance with the FIG. 1 apparatusand process thereof;

FIG. 28 is a cross-sectional view showing the engaged co-acting sealingheads at a moment in the welding cycle when a hot gas stream is beingapplied thereby to form the end welds on the bags;

FIG. 29 is a cross-sectional view partially through FIG. 18, taken alongreference line 29--29, thereof, and particularly illustrates thepreferred assembly for delivering hot welding gas to the sealing heads;

FIG. 30 is a cross-sectional view through FIG. 29, as taken alongreference line 30--30, thereof;

FIG. 31 is a cross-sectional view through FIG. 18, taken along referenceline 31--31, thereof, and particularly illustrates the preferredassembly for delivering cooling gas to the sealing heads, together withthe structure of one of the two revolving gusseting arms for providingmechanical assistance in side gusseting bags made according to the FIG.1 apparatus;

FIG. 32 is a cross-sectional view through FIG. 31 as taken alongreference line 32--32, thereof,

FIG. 33 is an enlarged partial view which illustrates a modification tothe filling mandrel designed to create a high velocity stream tocontinuously wash over the inside surfaces of the bag;

FIG. 34 is a cross-sectional view through FIG. 33 as taken alongreference line 34--34 thereof;

Intent Clause

Although the following disclosure offered for public dissemination isdetailed to ensure adequacy and aid understanding, this is not intendedto prejudice that purpose of a patent which is to cover each newinventive concept therein no matter how it may later be disguised byvariations in form or additions of further improvements. The claims atthe end hereof are intended as the chief aid toward this purpose, as itis these that meet the requirement of pointing out the parts,improvements, or combinations in which the inventive concepts are found.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A general teaching of the illustrated apparatus and process hereof isdescribed in relation to FIG. 1 through 7. Referring first to FIG. 1,apparatus generally designated as 10, includes an unwind assembly 12which rotatably mounts a rolled up web 14 of single or multi-ply,thermally sealable material. The web is continuously drawn off theunwind assembly at a constant rate by means to be described and undertension which is controlled automatically by a drag applying unit 16.The web is initially directed generally upwardly about idler feed rolls18 and 20 to an idler approach roll 22. The approach roll feeds the webat a controlled angle to a tube former 24, from whence it is drawndownwardly therethrough. The tube former continuously wraps or rolls theweb about a hollow filling mandrel 26 to provide a continuous verticaltube having its marginal or longitudinal edges overlapped. Theoverlapped edges are continuously welded together by a hot gas, verticalseam welder 28v. The fresh weld or seal is generally immediatelypartially cured by an impinging cooling gas supplied through a chillinghead 30 mounted underneath seam welder 28.

The tube is then drawn through a bag sizing cage 32. The sizing cageincludes opposed, continuous chain assemblies or vertical conveyors 34and 36, which are spaced to define a vertical cavity 38 through whichthe tube passes. The conveyors have mounted thereto and convey acontinuous series of slats 40 which define the effective width of cavity38; and also mount and convey a predetermined number of co-actingsealing heads 42 and 44, respectively. The sealing heads regularly cometogether to mate at a point below the lower terminating end of thefilling mandrel, and grasp the tubing therebetween, each time forming atemporary bottom, while continuously drawing or pulling the tubedownwardly to provide successive product receiving spaces in the tube.Simultaneously the sealing heads transversely cut and weld the tubing atregular intervals and cool the welds, before disengaging and beingreturned to repeat this cycle. The bags as they are manufactured, aredeposited onto a horizontal conveyor belt 56 operating underneath thesizing cage.

The bag mandrel 26 is arranged generally concentrically within, andextends axially both above and below the tube former. In the region ofthe tube former and thereabove, the filling mandrel is of cylindricalcross-sectional shape. Beginning near the lower extent of the tubeformer, the filling mandrel gradually changes to an ultimateconfiguration at its terminating lower end portion 46, as seen in FIGS.5-7 (see also FIGS. 10-12). The end portion 46 comprises opposed,generally flat sidewalls 48 and 50 connected by opposed, inwardly formedV-shaped end sections 52 and 54. This transformation in shape is toassist gusseting the tube in a manner as will be described. Also to thispurpose, end portion 46 is peripherally bounded by horizontalrestraining elements or means comprising horizontal restraining bars 60and 62, extending in close parallel relationship with sidewalls 48 and50, respectively; and gusseting rollers 64 and 66 disposed partiallywithin the inwardly formed end sections 52 and 54, respectively.

A product holding chamber 68 is affixed to the top of the fillingmandrel through means of flanged ends 70 and 72 in these pieces,respectively. The holding chamber communicates with the filling mandrelthrough a slide gate 74 operated through an air cylinder 76. The holdingchamber contains a dump bucket 78, which is suspended by attachment tothe arms 80 (only one showing) of a weighing scale 82. The dump bucketis released by a hinged bottom trap door 84, through an air cylinder 86and bracket connection 88. An electronically controlled surge hopper,shown partially at 90, or another suitable product introducing means, isconnected into the top of the holding chamber. The holding chamber isadapted to be evacuated by a high capacity, low vacuum evacuation fan92. The filling mandrel is adapted to be evacuated, independently of theholding chamber, by a high vacuum, low capacity evacuation fan 94.

The repetitive filling cycle of apparatus 10 is initiated by thetransfer of product from the surge hopper into the dumping bucket. Thescale 82 automatically weighs the product and at the proper momentelectronically signals the surge hopper to gate closed. The weighedproduct load is then dumped from the bucket onto slide gate 74 where itremains for a brief holding interval. During this interval, the productload is subjected to an evacuation step drawn through fan 92. Preferablyboth the fans 92 and 94 operate continuously to minimize cycle times.The evacuation of the holding chamber serves the purpose of removingentrained air from the product load. In order to optimize this endresult, the holding chamber is preferably evacuated to the maximumextent compatible with the limits of subsequent bag filling steps. Theselimits are determined mostly by the kinetic energy available fromdropping the product load from the elevation of the slide gate. Theproduct load, briefly, must have sufficient energy to quickly "shock" or"pop" the tube open and be received therein in proper timing to themating of the sealing heads, as will be explained more fullyhereinafter.

The remainder of the filling cycle is shown progressively in FIGS. 2through 5. In the FIG. 2 illustration, the product load is showndeposited on the slide gate at the instant just prior to dumping. Theholding chamber and the filling mandrel are both under internalevacuation. The degree of vacuum is greater in the filling mandrel dueto the relatively higher vacuum draw capability of fan 94. The tube atthis instant is sucked tightly against the sides of the filling mandrel,and is collapsed tightly upon itself therebelow due to the inwardbearing of atmospheric pressure.

FIG. 3 illustrates the filling cycle after opening slide gate 74, andinitial entry of the product load into the tube. An instant after theslide gate opens, the lower vacuum maintained in the holding chambertends to dominate over the filling mandrel to partially relieve thevacuum induced stress on the tube. The stress is momentarily relieved atleast sufficiently for the energy of the product load to open thecollapsed tube, and for the product load to be received quicklytherewithin. The evacuation fan 94 is designated as a low capacity fanin the sense that this fan does not have the capacity to recover fastenough after the slide gate opens, to prevent the necessary degree ofrelief on the tube. The energy of the product load is essentially theenergy of the elevational drop of the load, as influenced by thedownward sucking effect applied to the product load by the unbalancedvacuum pressures in the filling mandrel and holding chamber at theinstant the slide gate is opened. This energy must overcome thepressures bearing inwardly on the tube, and most optimally distends thetube sufficiently to fully accept the product load before the entiretyof the bag has passed the filling mandrel. The mandrel will in thismanner shield the upper welding surfaces of the bag from directengagement with the product. Inherently also, the product load ismomentarily packed toward the bottom of the bag, in a position to beforced upwardly by the squeezing action of the sizing cage, as will beexplained more fully hereinafter. The timing of this latter stepprovides the momentary condition of a margin of free space at the top ofthe bag, thereby lessening any chance of an interference between theproduct load and the sealing heads. By the same token, the bag is mademore receptive to the formation of neat appearing side gussets thereinby a procedure to be described. The consequence that must be avoided, inany event, is backup of the product load into the filling mandrel to anyextent as would cause a delayed filling action, whereby product woulddribble from the mandrel, and become interposed between the sealingheads at the instant the same close or clamp across the tube.

The filling cycle is shown toward its last stages in FIG. 4. The sealingheads 42 and 44 are ready to engage underneath the mandrel to form thetop end of the bag of this discussion, and simultaneously the bottom endof the bag next to be filled. The slide gate 74 is closed, and a newfilling cycle is already in process.

With the gate 74 in the closed position the high vacuum fan 94 dominatesover the filling mandrel to evacuate preferably as much air from the bagas is possible before the sealing heads close. The object is to tightenand firm up the bag to impart acceptable, and preferably optimumpalletizing and handling characteristics thereto. Moreover, a firm baguses less material, and the product load is in a sense densified by theevacuation steps so that it requires less packaging space. Air is morequickly removed from the top of the bag up to a certain depth into theproduct. However, because of an inherent pressure drop through theproduct, the removal of entrapped and entrained air from the bottom areaof the bag is hampered. The first vacuum stage applied in the holdingchamber, therefore, preconditions the product to better achieve thesought after objectives, under the conditions of fast, economical cycletimes.

Simultaneously, in controlled relationship with the timing or closing ofthe sealing heads, the sizing cage is acting to urge the productupwardly into the top portion of the bag. The sizing cage, overall,causes the product to flow and redistribute more evenly within the bagto give better shape and size uniformity thereto, and to negate internalvoid areas. The width of the sizing cage and its position is necessarilybalanced with the various factors controlling the upward flow of theproduct, in order that this step is compatible with the movement andclamping of the sealing heads.

The evacuation procedure described above is also used to form neat,shape imparting gussets to the bag simultaneously with its formation.Further on herein, it will be described how this same step can beemployed, in a modified practice hereof, to wash air over the insidesurfaces of the tube, to avoid weld or seal contamination by productdust when such is a problem.

However, referring specifically to the formation of the gussets, thisprocedure is depicted in FIGS. 5-7. These figures are tied in time toFIGS. 2-4, respectively, to which they relate as cross-sectional views.In FIG. 5, the tube is in a condition where it is pulled by vacuum forcetightly and flatly against the lower terminating end portion 46 of themandrel, imparting thereto a relatively neat gusseted configurationhaving essentially inwardly collapsed or inwardly tucked opposed sideportions as will ultimately comprise the gusset structure of the bag.

The subsequent shock of the dumped product load momentarily pulls thetube away from the mandrel as shown in FIG. 6. The memory of thegusseted shape, however, is retained in the tube by means of peripheralrestraint applied to the tube through restraining bars 60 and 62,cooperatively with gusseting rollers 64 ad 66. The memory permits orencourages the gussets to properly and neatly reform after each dump, asthe tube recovers and is sucked back tightly against the fillingmandrel, as seen in FIG. 7. In the preferred embodiment the shapedmandrel, with the assistance of the draw on the tube, thereby extendsthe gusseted structure into the area of the sealing heads 42 and 44which permanently weld the gussets into the bag as it is formed.

The gusset structure, added to the bag by practice of the abovecooperating restraining and vacuumizing steps, serves to square-up thebag giving it even better appearance, together with yet even furtherimproved stackability or ability to be palletized. Despite the fact thatthe gusset structure is permanently formed only after the tube has beenhighly stressed and filled, the gussets are surprisingly neat and strongdue to the manner in which the bottom and top welds are formed securingthe gussets. The welding technique is described in some depthhereinafter. As a general matter, however, the sealing heads first cutthe tube. The cut edges are then "bathed" in a directionally controlledstream of hot air or other gas, through a welding cycle shown in FIG. 1,after which the edges are bathed with cooler air for a short period asalso denoted in the same FIG. 1. No mechanical pressures are applied tothe seal such as would cause delineated lines of thinning orobjectionable preferential rupture lines. The welding technique isparticularly able to accommodate welding across varying numbers of pliesof material, as is the case with a gusseted tube, and form a strong weldat every interface.

UNWIND ASSEMBLY AND DRAG APPLYING UNIT

The unwind assembly 12 and drag applying unit 16 are shown in morecomplete detail in FIGS. 8 and 9. The rolled up web 14 is rotatablycarried on opposed plugs or collets 100 and 102 which insert into theopposite ends of the core of the roll. The plug 100 is freely rotatableon the end of a shaft 104 of a footed air cylinder 106, which is, inturn, fastened to a fixed horizontal mounting 108. The air cylindermoves plug 100 in and out for changing rolls, and the pressure of theplug against the roll is determined by regulating the pressure to theair cylinder. The opposite plug 102 is attached to the end of ahorizontal shaft 110. The shaft 110 is journably carried for freerotation by pillow bearings 112 secured to a fixed mounting 114. One ormore annular spacers 116 are adapted to be removably affixed to a collar118 on the back of plug 102. The removal or addition of spacers allowsthe operator to precisely align the center line of the web with thecenter line of the tube former for accurate web feed to the tube former.

A pump 120, which is part of the drag applying unit, operates off shaft110 by means of a chain and sprocket connection 122 therewith. Unit 16is a closed system including a fluid reservoir 124 which is elevatedabove the pump (see FIG. 9). The reservoir with the assistance of abracket 126, and the pump through a flanged end 128, are commonlyattached to a fixed vertical plate 130 which extends off fixed mounting114. An inflow pipe 132 communicates between the bottom of the reservoirand the pump, and an outflow or discharge pipe 134 between the pump anda 4-way solenoid valve 136, which is affixed to the top of the reservoirthrough a mounting piece 138. The solenoid valve, in turn, communicateswith the reservoir through a pair of variable restrictor valves 140 and142. Fluid is continuously fed through the inflow pipe to the pump, andthe discharge is returned to the reservoir via one or the other of therestrictor valves, depending on the valving position of solenoid valve136. The restrictor valves can each be needle valve assemblies which areadjusted to provide two settings. In one setting, the pump is requiredto work comparatively harder to return the fluid to the reservoir thanat the other setting. This determines the drag applied to the unwindassembly thus giving variable tension control over the web, i.e.,comparatively low or high tension depending at any certain time throughwhich restrictor valve the outflow from pump 120 is being diverted bysolenoid valve 136.

Web Registration Control

The drag applying unit 16 is designed to automatically maintain theproper registration of printed web material. Unit 16 works incooperation with three monitoring units or sensors, preferably electriceyes. One such electric eye 144 is placed in the sizing cage and recordsthe event of each passage of sealing heads 42, through an offset tab146, mounted to each head, and which breaks the circuit of this eye (seeFIGS. 1 and 24). Reading this event established a point that nevervaries, i.e., known point. Electric eye 144 dominates second and thirdspaced apart electric eyes 148 and 150 positioned to read printed markson the web as it comes off the roll.

Each time eye 144 reads the known point, it signals eyes 148 and 150 tolook for a mark. If the mark is at some point between the eyes, noresponse is made since the web is within the registration tolerances. Ifthe eye 150 nearest the tube former reads the mark, this indicates thatthe web is being over-stretched. This event signals the solenoid valve136 to switch over to the low restrictor valve automatically lesseningthe tension on the web to keep the same in proper register. Conversely,if the eye 148 farthest from the tube former reads the mark, the web isbeing under-stretched to maintain registration, and the solenoid valveis signaled to switch the outflow of the pump through the highrestrictor, automatically adding more stretch or tension to the web.

Tube Former and Air Bearing

Referring now particularly to FIGS. 10-12 and 15, the tube former 24 ismounted by right angle brackets 156 to the top of a horizontal platform158, and overlies a central opening 160 cut out of the platform. Thefilling mandrel is suspended through the tube former and opening 160 toextend below platform 158. Four vertical arms 162, 164, 166 and 168 arerigidly attached to the underside of the platform and extend downwardtherefrom alongside the filling mandrel. The arms 164 and 166 jointlycarry the restraining bar 60, whereas arms 162 and 168 carry theopposite restraining bar 62. The arms 166 and 168 also serve tojournably support the gusseting rollers 64 and 66, respectively. A pairof fixed frame arms 152 and 154 provide rigid support for the platform.

The tube former is preferably sheet metal which is formed to define agenerally hollow, cylindrical body having overlapped radially spaced,vertical edge portions 170 and 172. The edge portions are bracketedtogether by an adjustable bracket assembly 174. Assembly 174 allows thetube former to be expanded or contracted circumferentially to permit themaking of a slightly larger or smaller tube in response to variances inthe bulk density of the product load. The tube former includes pluralcut-outs 176 extending upwardly from its lower periphery or edge to givebetter flexibility to make this adjustment. Also the former is cut backat 180 underneath vertical edge portions 170 and 172 to permit almostimmediate access of hot welding gas to the tube.

The top edge 182 of the tube former can be generally near parabolic inshape. However, its exact optimum shape is determined experimentallydepending on the thickness and characteristics of web 14. Attached tothe top edge of the tube former in the manner of a rim, is a hollow,relatively small diameter tube 184. The tube includes numerousperforations 186 to provide an air bearing over which the web is floatedas it is being drawn through the former. The air bearing is continuallyfed by a regulated compressed air line 188, and complements fine webtension and registration control by reducing unwanted and uncontrolledfriction drag forces, and minimizes any prospect of drag induced damage,breakage, or unrecoverable over-stretching of the web.

Hot Gas Vertical Welder

The vertical seam welder 28 is best shown in FIGS. 10, 13 and 14. Theseam welder is carried on a horizontal slide 194 which movestransversely on a fixed slideway 196. The slideway is supported offplatform 158 by a rigid extension arm 198. An air cylinder 190 ismounted upon slide 194, and the arm 192 of the air cylinder is attachedby a rigid bracket 200 to slideway 196. The air cylinder operates slide194 to move the vertical seam welder to the approximate weldingposition, hold it there during operation, and automatically retract itto a safe distance when apparatus 10 is stopped to avoid burning theweb.

Fine vernier adjustment for the exact welding position or distance fromthe tube is controlled by use of a venier slide 202 moveabletransversely in a fixed slideway 204 which is attached to slide 194. Thevernier slide is operated by a low speed electric motor 206 affixed by avertical bracket 208 to the back of slide 194. The motor turns apreferably fine threaded screw 210 through a coupling 212. The screw isthreaded into the vernier slide to cause and hold fine adjustments.

The vertical seam welder includes a relatively flat, vertical hot gaswelding head or block 214 mounted to the forward end of a horizontalheater barrel 216 through an adapter 218. The opposite end of the heaterbarrel is attached to a holder 220 which, in turn, is affixed to slide202. The welding head includes internal diverging baffles 222 touniformly distribute the incoming gas flow to a narrow vertical slot 224which applies the gas to the tube. The slot 224 is centered on thelongitudinal center line of the overlapped edges of the tube. The heaterbarrel contains internal calrod gas heating elements (not shown), andreceives compressed gas from a pressure regulated line 226. The fillingmandrel includes an embedded vertical back-up strip 230, such as ofglass impregnated Teflon, aligned with slot 224 to prevent sticking ofthe tube to the mandrel.

A plate 232 is attached to the welding head, from which the chillinghead 30 is suspended by a pivot connection 234. The chilling head isadjustable for inclination with the vertical axis through means of acurved slot way 236 and tightening nut 238. The chilling head includes anarrow vertical slot 240 aligned vertically with slot 224 of the weldinghead, and is internally baffled at 242 to issue a generally uniformcolumn of cooling gas through slot 240. A pressure regulated compressedair line 244 operates the chilling head.

Operation of the Vertical Seam Welder

The compressed air line feeding the hot gas block must providesufficient velocity pressure to cause intimate contact between theinterfaces of the overlapped web in order to achieve optimum sealingresults. The temperature of the welding gas is balanced with the gasflow rate in order to supply enough BTU's to securely weld theinterfaces. If the air is too hot or the gas block too close,non-removable weld wrinkles appear. Under optimum conditions thevertical weld or seam 246 of the tube will initially show wrinkles asdepicted in FIG. 16, even after being partially cured by the chilledhead. However, when the weld is subjected to the stress of the productload, essentially all wrinkles are removed, and a smooth, virtuallyinvisible weld is achieved, as shown in FIG. 17. If properly formed andchilled, the finished weld line is invisible or near invisible even toclose inspection, and shows a virtually complete absence of wrinkling.The chilling head is operated to the benefit of the wrinkling removingeffects of the product load stress by not "over-curing" the weld.

The preferred means of temperature control is through a thermocouple inadapter 218 which signals the off-on operation of the calrod heaterelements. A vernier rheostat preferably controls the voltage to thecalrod heaters. Once the system is in balance, and the rheostat used toadjust the voltage to the calrods, minimum on-off operation is required,and a constant uniform gas temperature is available for welding.

The Bag Sizing Cage

The bag sizing cage is illustrated best in FIGS. 18 and 19. The sizingcage comprises vertical side plates 252 and 254 which are mounted byframe attachments (not shown) in opposed fixed relationship. The sideplates jointly carry four rotatable, horizontal shafts 256, 258, 260 and262, which are arranged rectangularly as viewed from the end. Each shaftcarries four axially spaced sprockets 264 of identical size. The shafts256 and 258 cooperate to mount and convey four side-by-side continuouschains 266 to form the vertical conveyor assembly 34. The verticalconveyor assembly 36 is formed by shafts 260 and 262, and fourside-by-side continuous chains 268. The conveyors are driven in unisonby an enclosed gear train 270 connecting between shafts 256 and 260, anda motor 272 which is coupled to the end of shaft 256, and affixed tovertical side plate 254 through a mounting piece 274. A hydraulic motoris preferably employed of a type having independent torque and speedcontrol. The chains 266 and 268 are preferably double pitch, wing typeroller chains to which the slats 40 are affixed through spacer elements276.

A floating vertical pressure plate 278 backs up the inner run of chains266, and cooperates in a manner to be described, with a fixed verticalrear support plate 280 which backs up the inner run of chains 268. Thefloating pressure plate is slidably supported on guide pins 282 that aremovable in guide bearings 284. The guide bearings, in turn, are fixedlymounted to a front vertical support plate 286. The latter also mounts aplurality of air cylinders 288 which operate the floating pressure plateon guide pins 282. Both the front and rear vertical support platesextend between and are supported by rigid attachment to vertical sideplates 252 and 254.

The Sealing Head Assemblies

The sealing head assemblies 42 and 44 are illustrated best by FIGS.20-28.

Referring first to sealing heads 44 (see particularly FIGS. 20-23), thesame each comprise an elongated rectangular mold block or holder 294. Aplurality of spaced apart arms or trunions 296 are rigidly affixed tothe back wall 298 of the mold block. The arms jointly carry a raisedmounting shaft 300, which, in turn, is pivotally connected to a backmounting plate 302 through spaced arms or trunions 304 extendingnormally off the plate. The plate 302 is affixed to roller chains 268 ofvertical chain assembly 36 to pivotally mount the molding block theretowith true alignment between the longitudinal axis of the block and thehorizontal axis.

Mounted to each end of the mold block is a fixed slideway 310 and 312,respectively. The mold block defines an elongated rectangular cavity 314which extends between slideways 310 and 312, and is open at the matingface 316 of the mold block. A movable cutter head 318 is containedwithin cavity 314. The cutter head is attached to slides 320 and 322,operating in slideways 310 and 312, respectively. The slides 320 and 322each include a roller type cam follower 324 and 326, respectively, whichare operated by vertical strip cams 328 and 330 affixed to the rearsupport plate 280 of the sizing cage. The slide and slideways eachinclude an exhaust port 332 and 334, respectively, which register in theforward cammed position to provide communication between cavity 314 andthe atmosphere. A pair of springs 336 connect between each slide andslideway to spring load the cutter head in a retracted rest position.

The cutter head 318 comprises an elongated central knife holding portion338 defining a narrow slot 340. The slot receives a knife blade or tubeparting element or means 342 that is removably secured therein bytightening and loosening set screw assemblies 344. The knife ispreferably a scalloped edge, single bevel knife, and is preferably heldin the slot at a slight grade over the length thereof, to achieve ascissor-type cutting effect. On each side of the knife holding portionare an aligned series of exhaust ports 346 separated by lands 348. Thelands give rigidity to the knife holding portion. The exhaust portsprovide communication between the face 350 of the cutter head and theregistrable exhaust ports 332 and 334 in the slides and slideways. Araised welding detent 352 is disposed between the terminatinglongitudinal edges 354 of the cutter head and the exhaust ports 346 oneach side of knife blade 342. The face of each detent 352 comprises abackup welding surface, the operative or effective portion of which isspaced from the portions of the tube under clamping pressure, forreasons as will become evident hereinafter.

Referring now particularly to FIGS. 24-26 the sealing heads 42 are inpart similar to sealing heads 44. Each include an elongated mold blockor holder 360 affixed pivotally to a mounting plate 362 through a shaft364 and trunions 366 and 368, respectively. The plate, in turn, isaffixed in horizontally level fashion to the roller chains of verticalconveyor assembly 34.

A hot gas inlet valve 370 is affixed to one end of mold block 360. Theinlet valve includes a raised center post 372 which is elevated abovethe top wall 374 of the mold block (in reference to the orientation ofthe mold block as it travels through the sizing cage). At the oppositeend of the mold block is a cold gas inlet valve 376 which is identicalto valve 370 except that it is reversely oriented so that the centerpost 378 thereof is offset beyond the bottom wall 380 of the mold block.The center post of each valve is slidably carried in a hollow valve body382. Each valve is operated by depressing the center post against aspring 384, to unseat a valving head 386 from an internal valving seat388. Each valve includes an external valving seat 390 about the centerpost thereof, for seating the valves against hot and cold gas deliveryheads, respectively, as will be described.

The mold block 360 defines an elongated open ended cavity 392. A hollowwelding head 394 is inset fixedly in cavity 392 and extends between thehot and cold gas inlet valves 370 and 376. The welding head includes awelding face 396 elevated from the floor of the cavity to define acontinuous channel 398. Each valve body 382 communicates with channel398 through a passageway 400.

The welding face 396 includes an elongated, vertical knife receivingwell or slot 402. The knife receiving well is bordered on each side byelongated strips 404 of resilient, high heat withstanding material,which provides a raised back-up surface for cutting.

Extending alongside each strip 404, but spaced therefrom, is a narrow,near continuous slot or stream forming opening or means 406. Narrowlands 408 interrupt and support the slots against possible warpage underhigh temperature welding conditions. The slots provide communicationbetween channel 398 and welding face 396 for directing the welding andcooling gases as will be explained hereinafter. The floor of the cavityunderneath the welding head is lined with a flat heat shield covering410 such as of Teflon. A sealing gasket 412 of relatively high heatwithstanding material is peripherally continuous about welding face 396and is interposed between the sidewalls of the cavity and the weldinghead. The gasket 412 is raised from the welding face to form a weldingspace or chamber upon mating of sealing heads 42 and 44 (see FIG. 28),in which the tube is essentially free of mechanical clamping pressures.

The Engagement and Operation of the Sealing Heads

The angle of approach of the sealing heads as they enter the sizing cageis adjustable by set screws 420 attached to each mounting plate 302 and362. This adjustment is held by springs 422 attached between themounting plate and the back of mold blocks 294 and 360, respectively.The angle of approach is set so that the sealing heads smoothly rolltogether and mesh properly (see FIGS. 27 and 28). The sealing heads 44each mount a set of four over and under guide rollers 424, respectively,through bracket attachments 426. The guide rollers assist to keepregister between the sealing heads in the clamped position by engagingfixed locking strips 428 on the bottom wall 380 of the opposite sealinghead 42, and fixed break-away brackets 430 on the top wall 374 thereof.The break-away brackets particularly will prevent the sealing head 42from slipping ahead of the sealing head 44, at the moment the same beginto part or disengage at the bottom of the sizing cage.

The clamping pressure between the sealing heads is controlled by thefloating pressure plate 278 with the assistance of rear support plate280, through regulating the line pressure to air cylinders 288 at theback of the pressure plate. The clamping pressure firmly seats sealinggasket 412 against the mating face of mold block 294, forming anessentially gas tight seal therewith, along opposed clamping zones orareas that extend transversely across the width of the tube, and whichare separated in the longitudinal direction, to define the upper andlower limits of the welding chamber.

Almost simultaneously with the clamping of the film between the sealingheads, the cam rollers on slides 320 and 322 engage strip cams 328 and330, respectively. The slides force the cutter head forward on slideways310 and 312, causing knife 342 to cut or part the tubing at welding face396. The detents on the cutter head draw the parted edges or cut ends432 and 434 of the tube away from the knife well as the knife moves tothe extreme forward position, thereby separating and defining a spacebetween the cut ends which communicates with exhaust ports 346.

At this moment, a moving hot gas supply head 436 moves vertically downupon the hot gas inlet valve 370, seating with the valve and depressingthe center post to force a heated welding gas, such as air into channel398. The operation and structure of the assembly supplying heated gas(and also the assembly supplying cooling gas in the latter part of theweld forming cycle) is described in some detail hereinafter.

The hot gas introduced into channel 398 escapes at high velocity throughthe directional slots 406, preferentially striking an extreme portion ofthe cut ends, remote from the clamped areas or zones, and then ventingfrom the welding chamber through the exhaust ports 346 on each side ofthe knife, and eventually to the atmosphere through the ports 332 and334 which register in the forward cammed position. The high velocitydirectional flow of the hot gas causes the cut plastic ends to lay downsmoothly against detents 352 by fluid or velocity pressure to intimatelycontact all interfaces of the cut ends. Outwardly of the detents, deadspaces or buffer areas 438 are defined in the welding chamber that areremoved from the primary flow of the heated gas streams. Retarded heattransfer and flow conditions exist in dead spaces to selectively preventheat deformation temperatures to extend to areas of the tube underclamping pressure.

The cut ends, due to the directionality and flow of the hot gas streamsare bathed in hot gas to a molten or near molten condition. The thinningof the cut ends is only a function of velocity pressure since the cutends are not mechanically restrained. The velocity pressure of thewelding stream is sufficient to intimately hold the layers of the cutends together to form a strong bond between all interfaces as sealing orwelding temperatures are reached. Too much velocity pressure can "washout" the cut ends, causing undesirable thinning. Most optimally,therefore, the velocity pressure is sufficient to hold the intimatecontact between the welding faces, but not so high as to thin and washout the cut ends, and the temperature of the hot gas stream iscontrolled to provide sufficient BTU's of heat to form a strong weld atall interfaces. If velocity pressure is correct, the welds can be formedshowing virtually no thinning throughout the entire extent thereof.Under proper welding conditions the unrestrained cut edges tend toshrink back to form a thickened or swollen weld of remarkably toughquality.

In order to provide a uniformly strong weld across the tube, the hot gaswelding stream must flow at essentially uniform velocity over the lengthof the directional slots. This is achieved by designing thecross-sectional area of channel 398 to be greater by a certain factorthan the combined cross-sectional area of the directional slots. In anexperimental shop apparatus, using a welding head 394 as illustratedherein, the most restricted cross-sectional area of this chamber wasdesigned to be approximately four times the area of the combinedcross-section of the directional slots. This factor of four was adequatein this particular design to achieve essentially uniform flow conditionsprovided a minimum threshold pressure was maintained in the channel. Thethreshold pressure is that at which the channel is able to readily feedthe directional slots without suffering a pressure drop from the infeedend thereof to the opposite end of the chamber.

At the end of the welding cycle, the moving hot gas supply headdisengages, releasing the center post, thereby closing the hot gas inletvalve.

Near simultaneously, a movable cold gas supply head engages theunderside of sealing head 42, to open cold gas inlet valve, andintroduce a cooling gas into channel 398. The cooling gas stream isdirectionally applied to the welds to cure the welds sufficiently toaccept the product load without damage to the weld. Refrigerated gas canbe used to achieve high speed cooling cycles.

The cold gas supply head then automatically disengages, closing the coldgas inlet valve. The cammed knife holder reaches the end of the stripcams, causing the cutter head to retract, and withdrawing knife 342 fromknife well 402. The sealing heads then release, depositing the finishedbag on the outfeed conveyor 56.

Hot and Cool Gas Supply to Sealing Heads

The hot gas supply assembly is shown as reviewed from the top in FIG.18, as denoted generally by reference numeral 446, and front and sideelevational views thereof are presented in FIGS. 29 and 30.

The hot gas supply assembly comprises the hot gas supply head 436 whichis mounted for reverse movement in the vertical direction by fixedattachment to a slide 448 which moves on a fixed slideway 450 mounteddirectly to vertical side plate 254.

The slide is operated by a vertical air cylinder 470 which is rigidlyaffixed to vertical side plate 254 through a reinforced mounting 472.The arm 474 of the air cylinder moves the slide through periodic contactwith a shock absorber 476 which is mounted to the middle part of slide448 through a right angle bracket 478.

A vertical telescoping tube 444 is connected to the underside of thesupply head and receives compressed gas from a pressure regulated line452. The stationary part 454 of tube 444 is supported by attachment tovertical side plate 254 through a holder element 456, and a bracketplate 458. The telescoping tube communicates through a passage 460 inthe supply head, with a pair of side-by-side calrod heating units 462and 464 affixed to the top of the supply head. The compressed gas isdelivered up the telescoping tube, through passage 460, up the calrodheater element 462, then across to the opposite calrod rod element 464,through a connector 466, from whence it moves back downwardly to thesupply head, and eventually out an outfeed port 486. The outfeed port isaligned vertically with the hot gas inlet valve, and centrally mounts aninternal actuating post (not shown).

The cycle begins with the air cylinder arm extended, which supports thesupply head above sealing head 42. At the proper moment, the aircylinder shaft is retracted, causing the head to slide downwardly andengage the hot gas valve, automatically opening the valve throughcontact between the actuating post, and the center post of the valve.The supply head will continue to ride the sealing head downwardly untilthe shock absorber impacts the reacted shaft of the air cylinder,automatically disengaging the supply head from the sealing head at theproper moment. The air cylinder then returns the supply head to thestarting position in time for the next cycle.

Preferably a solenoid valve (not shown) is employed to operate thecompressed gas line 452 for the duration of the welding process, andthen to automatically valve the line closed. The temperature of the hotwelding gas is preferably monitored and regulated through athermocoupling and a temperature controller (not shown).

The cold gas supplying unit which is denoted generally by ReferenceNumeral 480 in FIGS. 18, 31 and 32, is much like the hot gas unitdescribed above, except it doesn't include heating elements or a shockabsorber to protect the heating elements from jarring. It includes acool gas supply head 482 affixed to a slide 484 that moves vertically ona fixed slideway 486. The fixed slideway is mounted directly to thevertical side plate 252.

A second vertical air cylinder 488 is affixed to the vertical side plate252, near the top edge of the side plate, by a yoke and rigid armconnection 490 therewith. The arm 492 of the air cylinder extendsdownwardly to connect with and operate the supply head 482 on slide 484.A second vertical telescoping tube 494 includes an upper stationary part496 that is affixed to the vertical side plate 252 through a holderelement 498; and a movable part 500 that connects into supply head 482.A regulated compressed gas line 502, controlled preferably by an off-onsolenoid valve (not shown), supplies compressed gas through thetelescoping tube to the supply head. The gas eventually emerges out anoutlet port 504 on the top surface of the supply head. An actuating post(not shown) is centered in the outlet port.

To begin the cooling cycle, the air cylinder arm 492 is in the retractedposition, lifting the supply head 482 to an elevated starting position.As each sealing head 42 periodically descends in the sizing cage, iteventually engages the elevated supply head 482, and will ride the samedownwardly in aligned relationship so that the actuating post depressesthe cool gas inlet valve. Simultaneously the gas line 502 is operated tointroduce pressurized cooling gas to channel 398 to feed slots 406. Atthe termination of the downward run, and after a moments pause to allowthe sealing head 42 to clear, air cylinder 488 is operated to return thesupply head to the starting position to repeat the cycle.

Programmer and Mechanical Gusseting Arms

A horizontal timing shaft 510 shown near the top of FIG. 18, and incross-section in FIG. 31, is jointly carried by vertical side plates 252and 254. The timing shaft is rotatably driven off shaft 260 by a timingbelt 512, and pulleys 514 and 516. The pulleys are of a ratio so thatthe timing shaft turns 1 revolution per linear movement by the verticalconveyors equal to one bag length.

A programmer 518 is mounted to the exterior side of vertical side plate254, and is encased in a cover member 520. The programmer is illustratedsomewhat schematically, and includes a series of aligned programmingcams 522 (only one shown) which are rotatably driven by the timing shaftthrough a right angle drive 524. The cams operate a series or panel oflimit switches 526 mounted on a switch plate 528, to thereby control allthe decision making functions and programming of apparatus 10.

A pair of gusseting arms 530 and 532 are affixed to the rear supportplate 280 through bearing housings 534 and 536, respectively. Thegusseting arms are revolvably supported in the bearing housings, and aredriven off the timing shaft by means of second and third right angledrives 538 and 540, respectively, also affixed to the rear supportplate, and associated gear connections 542 and 544, respectively. Aone-to-one gear ratio is employed, whereby the gusseting arms turn onerevolution for each revolution of the timing shaft.

The gusseting arms are optionally provided, since the same areunnecessary where the operation permits the afore-described gussetingprocedure to be completed by unassisted vacuum force. However, forcertain fine grained and/or dusty products, a limiting condition on theuse of vacuum force will be reached if objectionable amounts of theproduct are drawn of through evacuation fan 94. Where the threshold ofthis condition is reached at a vacuum force less than that necessary toform neat gussets, mechanical assistance in forming the gussets can beemployed, together with that degree of vacuum draw available under thelimited conditions.

The gusseting arms are operated to revolve continuously clockwise andcounterclockwise, respectively, and are timed to simultaneously engagethe opposite sides of the bag and be generally at the horizontal or mostinward position at the moment the sealing heads mate, preferably at aspacing of about one-half inch (1.27 cm) below the sealing heads. Thesearms serve to assist in quickly setting the depth of the gussets, and toclear wrinkles from the area of the gussets just prior to the mating ofthe sealing heads.

Modified Filling Mandrel

A modified filling mandrel 26a which is shown in FIGS. 33 and 34,includes a slide strip or bar 546 disposed in spaced, peripherallycontinuous relationship about the lower terminating end portion 46a ofthe filling mandrel. The strip is rigidly connected to end portion 46aby spacer elements 548. The clearance is preferably about one-sixth toabout one-eighth of an inch, (1.6 to 3.2 mm) and is designed to leave anopen route or passage for a high velocity stream of air to be suckeddownwardly between the filling mandrel and the tube, under the conditionof internal evacuation of the filling mandrel. The high velocity streamcontinuously washes the inside surfaces of the tube to prevent settlingof the product dust and debris thereon, thus retaining the surface in amore virgin or non-contaminated state for sealing or welding.

EXAMPLE I

The apparatus and the process hereof is practiced to make industrialbags from various single and double ply webs of 401/4 inches (102.24cms) in width. The webs in all instances comprise a modifiedpolyethylene thermoplastic material, and range in thickness from about 4to 8 mils (0.1 to .2 mm). The bags have a length of about 27 inches(68.6 cms), an internal volume of approximately 1 cubic foot (28liters), and are each filled with a product load of polyethylene beadsweighing approximately 50 pounds (22.65 kgs). The production rate is sixbags per minute. A vacuum of 31/2 inches (8.9 cms) H₂ O is drawn on thefilling mandrel to gusset the bags without mechanical assistance. Thevertical seam welder supplies heated air to a 1 inch overlap on the tubeat approximately 320° F. (160° C.) using a one-fourth inch (0.64 cm)I.D. supply hose operated at a line pressure of about 20 to 22 psig(2.4-2.54 kg/sg cm). The sealing heads weld at a temperature of betweenabout 425° to about 475° F. (218° to 246° C.), and are supplied from a11/4 inch (3.2 cms) I.D. hose, operated at approximately 25 pounds psig(2.75 kg/sg cm) line pressure. The initial blast of heated welding gasis presumed to be at a higher temperature than the control instrumentreads. The thermocouple does not accurately monitor instantaneouschanges in temperature, and the initial blast comprises residual airthat has dwelled in the calrod heating elements. The duration of thewelding and cooling cycles are approximately 11/2 to 2 seconds each. Thecooling gas is non-refrigerated or ambient air supplied from a 40 poundpsig (3.8 kg/sg cm), compressed air line. The air bearing is operated at60 psig (5.2 kg/sg cm) and comprises tubing of five-sixteenths inch (0.8cm) O.D., and one-fourth inch (0.64 cm) I.D.

Satisfactory industrial bags are produced with a high degree ofrepeatability. The end seals or welds are characteristically curled andthickened, and show virtually no delineated or pronounced lines ofweakness. The end welds are approximately one-fourth inch (0.64 cm) inwidth and strong across the entire extent of the bags even at the pointsof abrupt thickness change. The vertical seam or weld is varied fromabout one-half to three-fourths inch (1.27 to 1.9 cm) in width. Thisweld can also be made with a high factor repeatability from bag to bag,and characteristically shows no wrinkling and is invisible or nearinvisible to close visual inspection.

EXAMPLE II

The general operating conditions of Example I are observed in thisExample II with the exceptions that the product load comprises Kedlorhigh protein stock feed, and secondly, the filling mandrel is modifiedgenerally according to FIGS. 33 and 34 to incorporate a strip 546. Bymeans of this modification, a high velocity stream is made availablethat continuously washes the inside surface of the tube. The stream isadequate to provide a sufficiently clean surface to achieve good weldingresults, even though the described product includes excessive dust.Without the modification dust contamination produces nonhomogeneouswelds.

EXAMPLE III

Various web materials of both single and multiple plies formed into atube using an overlapped longitudinal seal, and the tube is gusseted onopposite sides. The various tubes (in an unfilled state) are thenclamped between co-acting sealing heads operating under the generalprinciples of this invention, to form a transverse weld to secure theend of the tube. Successful welding results are achieved over a widerange of web thicknesses and materials as tabulated below.

    __________________________________________________________________________                                Thickness Variation                                                           Along Length of                                                               Weld Line                                                                     Minimum Maximum                                   Web Materials               Thickness                                                                             Thickness                                 __________________________________________________________________________    3 Mil (.08) LDPE (single ply)                                                                              6 Mil (.15)                                                                          12 Mil (.3)                               3 Mil (.08) EVA/3 Mil (.08) EVA (two ply)                                                                 12 Mil (.3)                                                                           24 Mil (.6)                               4 Mil (.1) EVA/4 Mil (.1) EVA (two ply)                                                                   26 Mil (.4)                                                                           32 Mil (.8)                               4 Mil (.1) LAM/8 Mil (.2) LDPE (two ply)                                                                  24 Mil (.6)                                                                           48 Mil (1.2)                              8 Mil (.2) LDPE/4 Mil (.1) LAM/8 Mil (.2)                                     LDPE (three ply)            40 Mil (1.0)                                                                          80 Mil (2.0)                              3 Mil (.08) LDPE/4 Mil (.1) Vinyl/2 Mil (.05)                                 LDPE (three ply)            26 Mil (.66)                                                                          52 Mil (1.32)                             3 Mil (.08) DCPP/3 Mil (.08) LDPE/3 Mil (.08)                                 MDPP (three ply)            18 Mil (.46)                                                                          36 Mil (.9)                               4 Mil (.1) EVA/LDPE Impregnated Nylon Scrim/4                                 Mil (.1) EVA (three ply)    36 Mil (.9)                                                                           72 Mil (1.8)                              6 Mil (.15) LDPE/LDPE Impregnated Cotton Cheesecloth                          Scrim/6 Mil (.15) LDPE (three ply)                                                                        34 Mil (.86)                                                                          68 Mil (1.73)                             4 Mil (.1) LDPE/4 Mil (.1) LDPE/5 Mil (.13) LDPE                              (three ply)                 26 Mil (.66)                                                                          52 Mil (1.32)                             __________________________________________________________________________     *LDPE - Low density polyethylene                                              EVA - Ethylene vinyl acetate                                                  MDPP - Medium density polypropylene                                           LAM - A co-extruded film of LDPE/EVA/Saran/EVA/LDPE                           Figures in parentheses are millimeters                                   

What is claimed is:
 1. In the method generally wherein web material iscontinuously drawn off a supply roll and converted into a continuouslymoving tube, simultaneously with the periodic entry of the product intothe tube, and the collapsing and transverse sealing of the tube atregular intervals to form therefrom filled bags, the steps to registerregularly occurring printed matter on the material with respect to theposition of the transverse seals comprising: reading a position that isfixed with respect to the position of the transverse seals, generating asignal responsive to reading the fixed position to activate spaced apartsensing means located in the region between the tube former and thesupply roll, decreasing the unwinding tension on the web should thesensor closest to the tube former read a registration mark on the web,increasing the unwinding tension on the web should the sensor farthestfrom the tube former read the registration mark, and maintaining theunwinding tension on the web static during periods in which such markfloats between such sensors and therefore is not read by either.
 2. Inapparatus wherein web material is continuously drawn off a supply rolland converted by a tube forming means into a generally vertical,continuously moving tube, simultaneously with the periodic entry ofproduct into the tube, and the collapsing and transverse sealing of thetube at regular intervals to form therefrom filled bags, the improvementwhich comprises, means to register regularly occurring printed matter onthe material with respect to the position of the transverse seals:including, a first sensing means adapted to read a position that isconstant with respect to the position of the transverse seals, a secondsensing means between the tube forming means and the supply roll, athird sensing means between the tube forming means and the secondsensing means, and spaced from the latter in the longitudinal direction,means to generate a signal upon the first sensing means reading theconstant position and to relay the signal to the second and thirdsensing means to activate the same to look for regularly occurringregistration points on the material, and means to vary the unwindingtension of the web downwardly responsive to the control of said thirdsensing means, and upwardly responsive to the control of said secondsensing means.
 3. The apparatus of claim 2 wherein said means to varythe unwinding tension on the web comprises a pump driven by said supplyroll, a first restrictor valve, a second restrictor valve, means fordiverting the flow of fluid from the pump through one or the other ofsaid restrictor valves, said diverting means being controlled by thesecond and third sensing means whereby the tension on the web iscontrolled at any given time depending on which restrictor valve theflow of the pump is being diverted through.